The specific aim of the Phase I and Phase II research program will be to design and build an "open", split pair coil, high field (>1 .5T), cryogen-free MRI magnet. The key innovation that will make this goal feasible is the development of an advanced, high performance, round high temperature superconductor capable of operation at 20 Kelvin. Operating at a temperature of 20K will allow cooling of the magnet by conduction with a mechanical cryocooler. A cryogen free system does not require the vacuum and cryostat space and therefore will allow the magnet designer to use a split pair coil configuration for an open system for easier access to the imaging subject and the central imaging volume. An open magnet also provides more patient comfort by removing the claustrophobic "tunnel" of conventional cylindrical superconducting magnets. The cryogen free structure might also allow the magnet to be used in the horizontal and vertical position, allowing imaging while the patient is in the standing position. The benefits of open, superconducting MRI magnets are being realized daily. In 1994 a superconducting GE open magnet system was installed at the Brigham & Women's Hospital. Since then researchers at the Harvard Medical School believe that the machine will pay for itself by increasing the speed and accuracy with which surgeons can do biopsies on cancerous tumors. Also, by allowing surgeons to biopsy tumors that cannot be diagnosed by conventional methods, the new technique could save patients not only the costs but also the pain and discomfort of needless or inappropriate therapies. Another application of an open MRI is the use in osteoporosis diagnosis. In this case, the calcaneum of the feet of the patient is placed into the MRI machine. Most patients examined are typically elderly with very little mobility and cannot withstand significant discomfort by positions required in the conventional MRI system. A split coil configuration would then allow a much easier and more comfortable access to the volume of interest.